Dead tank circuit breakers are commonly found in substations and are operable to selectively open and close electrical connections contained within a sealed tank filled with dielectric material for reducing arcing.
Despite careful manufacturing practices, an assembled circuit breaker can contain undesirable foreign particles such as metal shavings from machined parts, dirt, etc. It is undesirable for these particles, especially metallic, electrically conductive particles to reside in the tank since, if such particles are permitted to remain free in the tank, they could cause undue arcing, flashing, or can be electrically charged and radially reciprocate within the tank, reducing the breakdown voltage of the circuit breaker.
Particle traps have been developed for trapping these foreign particles. Conventional particle traps are configured in three ways: external, integrated and interrupter offset. External particle traps are components that are fixed to the bottom tank in some manner to shield particles in the bottom of the tank from the electric field. However, external particle traps are subject to manufacturing and assembly of the shield. Additionally, they typically shield a relatively small region. Also, multiple attachment locations of the traps in the tank are required in order to account for phase rotation.
Integrated particle traps are a cast feature and typically include a single trough (running radially), a single cup, or single trough (running lengthwise of the tank) used to catch particles. Cups and troughs are susceptible to the electrical field reaching into the protected area and generating activity. A trough running with the tank length can always permit the electric field to enter. There are ways to avoid the field from entering the cup and the radial trough, such as making the depth significantly deeper than the width. This is not possible on some dead tank circuit breakers due to height restrictions. Therefore, another method is to minimize the width of the trap such that the depth to width ratio is optimized. However, this method leads to a greater probability of particles not entering the integrated trap. Additionally, multiple troughs are typically needed to account for phase rotation, which increases the complexity of the tank.
Another method of controlling foreign particles in a circuit breaker tank is to offset the axis of an interrupter from the tank axis such that the distance between the interrupter and the tank is greatest on the bottom of the tank and smallest on the top of the tank. This method cannot completely account for phase rotation that must be compensated for in the configuration of the tank diameter. This configuration also requires changes to the mounting of the interrupter and other components to account for the required offset.
Thus, there is a need to provide a circuit breaker tank that is configured to reduce the effects of foreign particles in the electric field along the entire bottom of the tank regardless of phase rotation and without interrupter offset.